1. FIELD OF THE INVENTION
The present invention relates to epitaxial growth by means of the ELO (Epitaxial Lateral Overgrowth) method and, more particularly, to the method for forming the SOI structure which allows an easy control of epitaxial growth.
2. DESCRIPTION OF THE PRIOR ART
There is a way of forming an epitaxially grown layer on an insulating layer in order to make a high-speed device in an integrated circuit. The structure thus formed is called the SOI (Semiconductor On Insulator) structure.
FIG. 1 illustrates the conventional SOI technique using the ELO (Epitaxial Lateral Overgrowth) method ("Lateral Epitaxial Overgrowth of Silicon on SiO.sub.2," by D. D. Rathman et. al., JOURNAL OF ELECTRO-CHEMICAL SOCIETY SOLID-STATE SCIENCE AND TECHNOLOGY, October, 1982, p. 2303). First, a silicon dioxide layer 4 is grown on top of a semiconductor substrate 2. Then, resist 6 is applied to the silicon dioxide layer 4, as shown in FIG. 1B. The resist 6 is subjected to exposure and development using a photomask to thereby form an opening 8 (FIG. 1C). Further, the silicon dioxide layer 4 is etched using the resist 6 as a mask to thereby open an opening 10 (FIG. 1D).
This is followed by selective epitaxial growth of silicon from the opening 10 (FIG. 1E), so that an epitaxially grown layer 12 shown in FIG. 1F is formed on the silicon dioxide layer 4.
However, the conventional SOI technique described above has the following problems.
First, this technique includes two directional epitaxial growth, that is in the longitudinal direction until the state of FIG. 1E and, subsequently, in the lateral direction. As a result, the epitaxial growth can not be readily regulated, making it impossible to realize the epitaxially grown layer having large area or sufficient thickness.
Second, the epitaxially grown layer thus formed tends to swell near the opening 10, not allowed to have uniform thickness.